Field of the Invention
The present invention relates to a developing apparatus, a cartridge, a process cartridge, and an image forming apparatus. The developing apparatus includes at least a developer bearing member that bears a developer. The developing apparatus sometimes includes, for example, a frame body for storing the developer and a conveying member that conveys the developer. The cartridge is a component in which a plurality of components in the image forming apparatus are integrated to be detachably attached to an image forming apparatus main body. The process cartridge includes at least an image bearing member that bears a developer image. In particular, a component in which the image bearing member and process means acting on the image bearing member are integrated is called a process cartridge. The image forming apparatus is an apparatus that forms an image on a recording material (a transfer material), and in particular, an apparatus that adopts an electrophotographic system.
Description of the Related Art
Conventionally, in image forming apparatuses such as an electrophotographic apparatus and an electrostatic recording apparatus, from the viewpoint of simplification of apparatus configurations and elimination of wastes, a cleaner-less system (a toner recycle system) has been proposed. In the cleaner-less system, a dedicated drum cleaner, which is surface cleaning means after a transfer process of a photosensitive body, in an image forming apparatus of a transfer system is removed. Therefore, an untransferred toner on the photosensitive body after the transfer process is cleaned and removed from the photosensitive body by a developing apparatus and collected into the developing apparatus.
In particular, cleaning performed simultaneously with development in the developing apparatus is called development simultaneously cleaning. The development simultaneous cleaning is a method of collecting the toner remaining on the photosensitive body after the transfer process with fog removing bias (a fog removing potential difference Vback, which is a potential difference between a direct-current voltage applied to the developing apparatus and the surface potential of the photosensitive body) during development in the next and subsequent processes. With this method, the untransferred toner is collected into the developing apparatus and reused in the next and subsequent processes. Therefore, it is possible to eliminate a waste toner and reduce labor required for maintenance. Since the image forming apparatus is cleaner-less, a cleaner mechanism is not separately provided. There is a significant advantage in terms of space. It is possible to greatly reduce the size of the image forming apparatus (Japanese Patent No. 4510493, Japanese Patent No. 4785407, Japanese Patent Application Laid-open No. 2004-354978, and Japanese Patent No. 4630703).
When the cleaner-less system is adopted, when the toner is recycled, it is likely that foreign matters such as paper powder enter the developing apparatus and an image failure is caused by the foreign matters. For example, a representative image failure is a streak-like image failure that occurs because the paper powder and the foreign matters are held between a regulating blade and a developing sleeve and a uniform toner layer is disturbed. Besides, it is also likely that black spots occur in a white background portion of paper or, conversely, white spots occur in a printed portion because the paper powder is developed together with the toner.
Therefore, as the developing apparatus adopted in the cleaner-less system, a one-component magnetic contact developing system is proposed (Japanese Patent No. 4510493). In this system, a magnetic developer (a magnetic toner) is born on a developing sleeve (a developer conveying member), which includes magnetic field generating means, and brought into contact with the surface of a photosensitive member to perform development. The magnetic toner in the developing apparatus is carried to the vicinity of the developing sleeve by a mechanical supplying mechanism or the gravity and finally supplied to the developing sleeve by magnetism. The magnetic toner supplied to the developing sleeve is regulated to a proper amount by the regulating blade disposed in contact with the developing sleeve and forms a uniform toner layer. DC bias is applied between developing rollers.
In such a developing apparatus, the magnetic toner is supplied to the developing sleeve using the magnetism. Therefore, it is possible to more preferentially supply the toner to the developing sleeve than the paper powder that does not have magnetism. Therefore, an image is less easily affected by the paper powder than in a cleaner-less system that adopts a non-magnetic contact developing method.
On the other hand, when it is attempted to increase the life of the cleaner-less system, fogging performance is sometimes deteriorated by recycling of the toner. While an image forming process is repeated, triboelectric charging characteristics of the toner are deteriorated. Proper electric charges cannot be applied to the toner by the regulating blade. As a result, fogging is sometimes worsened. The fogging means an image failure in which the toner is slightly developed in a white portion (an unexposed portion) that is originally not printed.
On the other hand, there is proposed a method of applying, to the regulating blade, bias (blade bias) on the same polarity side as the toner with respect to developing bias and providing a potential difference between the regulating blade and the developing sleeve to facilitate application of electric charges to the toner with an electric field in a contact region (Japanese Patent No. 4785407). The application of electric charges to the toner is facilitated by the blade bias. Even after a long period of use, the appropriate electric charges are applied to the toner. The fogging is less easily worsened.
On the other hand, a cleaner-less system that adopts a contact charging system, in which a charging roller is used, is proposed (Japanese Patent Application Laid-open No. 2004-354978). When the contact charging system is used in the cleaner-less system, a charging failure is caused by adhesion of the toner to the charging roller, which is a charging member. As a method of reducing the adhesion of the toner to the charging member, it is known to drive the charging member to provide a circumferential speed difference between the charging member and a photosensitive drum. It is also known to provide optical discharging means in view of stability of a charging process and memory removal.